I found a manual for the DC8T online, which includes the following statement that I assume is also applicable to the DC8Ti:
Regards,
-- Al
Connection of Earth or 'Ground' Lead:
Use of a shielded or screened loudspeaker cable will offer further performance advantages when used with the five-way terminal panel. The screening termination should be connected to the earth or ground (green) terminal on the loudspeaker and to the ground or earth connection on the amplifier. Alternatively if you are not using a screened loudspeaker cable but wish to utilise the earthing facility, run a single cable between the earth or 'ground' (green) terminal on the loudspeaker to the earth (ground) connection on the amplifier .
Regards,
-- Al